This invention relates to a method and apparatus for the solid phase crystallization and polymerization of polymers. The invention relates more particularly to a unique system for heating the polymers in the solid state to achieve the desired reactions.
Prior art systems of the general type involve feeding of cold amorphous granular polymer material to a crystallizer and, after substantial heat input, discharging of hot crystallized product. A particular apparatus for achieving the crystallization may comprise an indirect heat supply unit or a fluid bed. The SOLIDAIRE.RTM. or TORUSDISC.RTM. equipment manufactured by Hosokawa Bepex Corporation of Minneapolis, Minn. are examples of indirect heat supply units which may be utilized for achieving the solid phase crystallization and/or polymerization. In such systems, steam or other heated fluid is passed through rotors and/or jackets which are in contact with the vigorously agitated granular polymer material. Due to the contact with these hot surfaces, the polymer is heated to the necessary temperature for achieving the crystallization and polymerization reactions.
In a fluid bed system, for example units manufactured by Hosokawa Bepex, heated air is brought into contact with the polymer material. In order to improve heat transfer and to achieve the temperatures required for the crystallization reaction, indirect heating elements in the form of tube bundles or plate coils may be immersed in the fluidized material.
Although processing of polymers in accordance with prior art systems can be successfully achieved, there have been persistent problems associated with stickiness of polymer chips which exhibit adhesive characteristics during the solid phase crystallization and polymerization. This has been a long-recognized difficulty as discussed in U.S. Pat. No. 3,014,011, and a proposed improvement has been discussed more recently in U.S. Pat. No. 5,090,134. In the latter case, the prevention of agglomeration and caking is specifically discussed.